1. Field of the Invention
The invention relates to an illuminating system and in particular, to the arrangement of air-hole areas of an illuminating system.
2. Description of the Prior Art
Referring to FIG. 1, the conventional illuminating system 100 includes a system casing 110 and an illuminating module 120. The system casing 110 has a first air inlet 112 and a first air outlet 114. The illuminating module 120 is disposed at the first air outlet 114.
The illuminating module 120 includes a diversion casing 122, a light source 124, a heat sink 126, and a fan 128. The diversion casing 122 has a second air inlet 122a and two second air outlets 122b. The second air outlets 122b are corresponding to the first air outlet 114, and the fan 128 is disposed at the second air inlet 122a. The light source 124 includes a printed circuit board 124a and a plurality of light emitting diode elements 124b. The light emitting diode elements 124b are disposed at one side of the printed circuit board 124a and electrically connected to the printed circuit board 124a. 
The heat sink 126 is disposed at another side of the printed circuit board 124a and located within the diversion casing 122, and the heat sink 126 is thermally coupled to the printed circuit board 124a. The heat sink 126 includes a heat-dissipating plate 126a and a plurality of fins 126b. The printed circuit board 124a of the light source 124 is disposed at the heat-dissipating plate 126a. The fins 126b are disposed at the heat-dissipating plate 126a. Each of the fins 126b and the light source 124 are disposed at opposite sides of the heat-dissipating plate 126a, respectively. The fan 128 is disposed at the fins 126b. 
When the illuminating system 100 operates normally, the light emitting diode elements 124b generate light and heat and the fan 128 operates to generate an airflow C1. The airflow C1 enters the system casing 110 through the first air inlet 112, then passes through the second air inlet 122a, the heat sink 126, and then leaves the system casing 110 through the second air outlets 122b and the first air outlet 114.
However, when the fan 128 breaks down, the heat generated by the light emitting diode elements 124b may not be efficiently dissipated to the outside environment. Therefore, the illuminating module 120 may be damaged because it is overheated.